The conformation and stability of human Zn-alpha 2-glycoprotein in aqueous and methanolic solutions.
The stability of Zn-alpha 2-glycoprotein has been studied using UV-spectroscopy and circular dichroism with respect to the influence of temperature, pH, and solvent composition. It has been found that: (1) this protein contains a relatively high proportion of beta-sheet (60%) and a very low amount of other periodic structures as estimated from circular dichroic spectra; (2) at pH 7.4, the circular dichroic spectra change reversibly in the temperature range between 25 and 85 degrees C; small disturbances were observed at 265 nm; (3) with the assumption of the two-state process, the temperature of cooperative denaturation was Tm = 66 degrees C, van't Hoff's enthalpy of this process was 27 kJ mol-1; (4) up to pH 9.5 the dichroic spectrum appeared the same as at pH 7.4; (5) in the presence of methanol (vol. fraction 50%), no isodichroic points on the circular dichroic spectra were found during temperature denaturation; after cooling from 85 degrees C, the alpha-helix content was higher than in the native protein; (6) in the molecule of Zn-alpha 2-glycoprotein, 14 out of 18 tyrosines can dissociate with the instrinsic pK = 11.2; and (7) the temperature perturbation difference spectra yielded nonlinear delta A vs. T curves with temperature transition corresponding to the values found in the circular dichroic spectra; the numbers of chromophores exposed to the solvent as determined by the temperature difference spectra were: 4 tyrosines, 1 tryptophan, and 1 phenylalanine. In several aspects, a parallel has been found between Zn-alpha 2-glycoprotein and orosomucoid (acid alpha 1-glycoprotein), another plasma glycoprotein.
Karpenko
V
V
Charles University, Faculty of Natural Sciences, Department of Physical and Macromolecular Chemistry, Prague, Czech Republic. karpenko@prfdec.natur.cuni.cz
Kaupová
M
M
Kodícek
M
M
D002942:Circular Dichroism; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D000432:Methanol / Q000494:pharmacology; D011487:Protein Conformation; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D029589:Seminal Plasma Proteins; D012997:Solvents / Q000378:metabolism; D013053:Spectrophotometry; D013696:Temperature; D014443:Tyrosine / Q000378:metabolism; D014466:Ultraviolet Rays; D000090203:Zn-Alpha-2-Glycoprotein
D006023:Glycoproteins; D029589:Seminal Plasma Proteins; D012997:Solvents; D000090203:Zn-Alpha-2-Glycoprotein; D014443:Tyrosine; D000432:Methanol